content: /* ===========================================================
   * JFreeChart : a free chart library for the Java(tm) platform
   * ===========================================================
   *
   * (C) Copyright 2000-2012, by Object Refinery Limited and Contributors.
   *
   * Project Info:  http://www.jfree.org/jfreechart/index.html
   *
   * This library is free software; you can redistribute it and/or modify it
   * under the terms of the GNU Lesser General Public License as published by
   * the Free Software Foundation; either version 2.1 of the License, or
   * (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
   * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
   * License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
   * USA.
   *
   * [Oracle and Java are registered trademarks of Oracle and/or its affiliates.
   * Other names may be trademarks of their respective owners.]
   *
   * -------------------------
   * PolynomialFunction2D.java
   * -------------------------
   * (C) Copyright 2009, by Object Refinery Limited.
   *
   * Original Author:  Peter Kolb;
   * Contributor(s):   David Gilbert (for Object Refinery Limited);
   *
   * Changes:
   * --------
   * 23-Mar-2009 : Version 1, patch 2795746 (PK);
   * 28-May-2009 : Integrated in JFreeChart with modifications (DG);
   *
   */
  
  package org.jfree.data.function;
  
  import java.io.Serializable;
  import java.util.Arrays;
  import org.jfree.chart.HashUtilities;
  
  /**
   * A function in the form <code>y = a0 + a1 * x + a2 * x^2 + ... + an *
   * x^n</code>.  Instances of this class are immutable.
   *
   * @since 1.0.14
   */
  public class PolynomialFunction2D implements Function2D, Serializable {
  
      /** The coefficients. */
      private double[] coefficients;
  
      /**
       * Constructs a new polynomial function <code>y = a0 + a1 * x + a2 * x^2 +
       * ... + an * x^n</code>
       *
       * @param coefficients  an array with the coefficients [a0, a1, ..., an]
       *         (<code>null</code> not permitted).
       */
      public PolynomialFunction2D(double[] coefficients) {
          if (coefficients == null) {
              throw new IllegalArgumentException("Null 'coefficients' argument");
          }
          this.coefficients = coefficients.clone();
      }
  
      /**
       * Returns a copy of the coefficients array that was specified in the
       * constructor.
       *
       * @return The coefficients array.
       */
      public double[] getCoefficients() {
          return this.coefficients.clone();
      }
  
      /**
       * Returns the order of the polynomial.
       *
       * @return The order.
       */
      public int getOrder() {
          return this.coefficients.length - 1;
      }
  
      /**
       * Returns the function value.
       *
       * @param x  the x-value.
       *
       * @return The value.
       */
      @Override
      public double getValue(double x) {
          double y = 0;
          for(int i = 0; i < this.coefficients.length; i++){
              y += coefficients[i] * Math.pow(x, i);
          }
          return y;
      }
  
      /**
       * Tests this function for equality with an arbitrary object.
       *
       * @param obj  the object (<code>null</code> permitted).
       *
       * @return A boolean.
       */
      @Override
      public boolean equals(Object obj) {
          if (!(obj instanceof PolynomialFunction2D)) {
              return false;
          }
          PolynomialFunction2D that = (PolynomialFunction2D) obj;
          return Arrays.equals(this.coefficients, that.coefficients);
      }
  
      /**
       * Returns a hash code for this instance.
       *
       * @return A hash code.
       */
      @Override
      public int hashCode() {
          return HashUtilities.hashCodeForDoubleArray(this.coefficients);
      }
  
  }
  